Switch proxy for providing emergency stand-alone service in remote access systems

ABSTRACT

A switch proxy comprising a controller, a translations database and a switching fabric are connected to a trunk group between a remote terminal and its controlling local switching system. The switch proxy monitors control and alarm signals to and from the switching system on the trunk. In the event of loss of control signals from the host switching system, the switch proxy intercepts requests for service, etc. from a calling telephone connected to the remote terminal and performs a look up in the translation database. If the call can be completed without the controlling switching system the call is looped back to the remote terminal. The translation database is maintained by a switch proxy management system that receives change orders from the local exchange carrier. The switch proxy management system forwards relevant changes to the switch proxy&#39;s translation database in the field.

RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/257,140, entitled “Switch Proxy for ProvidingEmergency Stand Alone Service in Remote Access Systems,” filed on Oct.24, 2005, now U.S. Pat. No. 7,680,252. The present application alsoclaims priority to U.S. Provisional Patent Application 60/694,146, filedon Jun. 27, 2005.

BACKGROUND OF THE INVENTION

This invention relates to access systems as used in wireline telephonyand, more specifically, to a switch proxy for use in conjunction with anaccess system remote terminal to route telephone calls whencommunications between a remote terminal of an access system and itscontrolling switching system is lost.

Wireline telephone service providers use access systems to servetelephone subscribers that are not economically or practically serveddirectly from the nearest local switching system. Examples of accesssystems of this type include subscriber loop carriers and digital loopcarriers (or DLC's). An access system consists of a remote terminal thatis connected to a local switching system (or central office or CO) byone or more digital trunk groups. The remote terminal can be located ina field cabinet, where the telephone subscriber's traditional copperpair is created in nearer proximity to the subscriber's premises. Thiscapability improves the service that the subscriber receives andprovides the telephone service provider with an economic alternative tolong cable runs from the local switching system.

For engineering simplicity, remote terminals are typically designed tohave very little independent operational capability. They rely on thehost switching system for essentially all of the intelligence that wouldnormally be associated with origination, routing and completion of atelephone call. The subscriber lines terminate at the remote terminal,which converts the voiceband signals into digital signals that are, inturn, multiplexed over digital channels on the trunk lines between thelocal switching system and the remote terminal. The trunk lines alsocarry separate digital channels for control information. The localswitching system controls the remote terminal as if it were an extensionof the switching system. For example, dial tone is sourced from thelocal switch and the dialed digits are collected by it.

In this manner, service providers are afforded more options in providingtelephone service to subscribers. In particular, these access systemsprovide a much more economical approach to serve a small remotecommunity of subscribers than the use of expensive local switchingsystems or proprietary remote switching modules. Typically DLC systemssupport between 100 and 2000 subscribers.

The simplicity of aggregating all of the call control functionality inthe host switching system creates a problem in the art. That is, whenthe host switching system is unable to communicate with the remoteterminal, either through failure of components of the digital trunks orof the switching system itself, subscribers served by the remoteterminal no longer have any telephone service. Even though theconnectivity with the greater network is lost and the remote terminalmay be otherwise fully functional, the subscribers terminated on thisremote system still cannot communicate with one another. The severity ofthis problem may be confounded by the fact that these subscribers arefrequently served by this technology precisely because they are remote.These remote settings necessitate the use of local emergency respondersand limit other communications options (e.g., cellular telephony).Therefore, the ability to continue to locally switch calls betweensubscribers served by remote systems that have lost communications witha host switching system is an important public safety consideration.

In urban deployments, the loss of connectivity to an access system maybe only a minor inconvenience; nearby neighbors may be served fromanother system and cellular service will probably be available.Furthermore, urban densities allow for engineering the transportfacilities with extra capacity that allows for “fail over” to protectionfacilities.

In rural settings, the remote terminal may provide the telephoneservices for an entire community. These rural communities could be veryisolated from other communities and cellular service may benon-existent. Loss of communications between the host switch and theremote terminal in these circumstances could result in more seriousconsequences than in urban scenarios.

To mitigate the potential negative impact on public safety andcommunication among members of the community during such serviceoutages, some rural public utility commissions and other agencies havepromoted inclusion of Emergency Stand Alone (ESA) capabilities intelephone access systems. ESA capabilities typically include the abilityfor subscribers to dial 9-1-1 to reach public safety personnel and tocomplete telephone calls among the members of the local communityisolated by the service outage.

The Public Safety Answering Point (PSAP) is normally the location whereoperators answer emergency calls and dispatch first responders. Usually,telephone services to a PSAP are provided directly from a central officeand not from a DLC system. This is for a variety of reasons, includingthe fact that PSAPs generally require special trunks (e.g., CAMA trunks)to carry Automatic Number Identification (ANI) and Automatic LocationIdentification (ALI) information to emergency operators, and DLC systemstypically do not support such special trunks. Therefore, isolated ESAsystems (in emergency mode) will usually need to direct 9-1-1 calls toan alternative location, to a 9-1-1 designate, rather than to a PSAP.The 9-1-1 designate will, of course, need to be a subscriber served bythe ESA system while in emergency mode, a sheriff's substation or alocal fireman's home, for example, may be chosen for thisresponsibility.

Other suggestions in the prior art pertain to installation of a“miniature” switching system in the proximity of the remote terminal toserve as a local host. This approach is not only expensive butimpractical on several counts:

-   -   i) it changes the basic architecture of the exchange network,    -   ii) it increases the number of switches to administer and        maintain,    -   iii) it actually increases the probability of a service outage        by putting another switching system into the chain, and    -   iv) these remote terminals are frequently installed in field        cabinets where it may be impossible to install an additional        complex system.        Thus, there currently does not exist an economical or practical        scheme for providing emergency stand alone service to        subscribers served by the installed base of access systems. In        addition, this invention discloses methods by which a 9-1-1        designate may be informed when incoming calls are emergency        calls and be provided with information related to the caller        similar to that available to a PSAP operator to insure proper        handling of the call. In particular, the present invention        addresses these issues by providing a ESA-capable system that        enables 9-1-1 designates to be informed of the name, telephone        number and address of emergency callers during these service        outages.

SUMMARY OF THE INVENTION

This problem is solved and a technical advance is achieved in the art bya system and method that provides a switch proxy to control one or moreremote terminals when connection to a host switching system is lost. Aswitch proxy in accordance with this invention comprises a controller, atranslations database and a switching fabric, which are connected to thetrunk group between the remote terminals and the local switching system.The controller, translations database and switching fabric are soadapted and configured that: a translations database maintainstranslations for its associated remote terminal(s) and the switchingfabric has a capacity to switch calls among subscribers served by thatswitch proxy and its subtended remote terminals. Thus, no modificationof existing infrastructure, either in the switching system or the remoteterminal, is needed, except to introduce this switch proxy in the trunkgroup between the local switching system and the remote terminal.Indeed, neither the host switching system nor the remote terminal needbe aware of the existence of this switch proxy for proper operation.

In accordance with one aspect of this invention, the switch proxymonitors control signals on the trunk group between the remote terminaland its controlling switching system. In the event of loss ofcommunication of control signals on the trunk group, the switch proxyseizes control of all or a subset of the trunk group and re-establishesthe interface with the remote terminal with itself acting as the “hostswitching system” thereby becoming the proxy for the actual host system.To the remote terminal, it appears as though a short outage with theswitching system has occurred followed by restoration of some or all ofthe services from the switching system. The switch proxy interceptsrequests for service, etc., from a calling telephone connected to theremote terminal and performs a look up in the translation database. Ifthe call can be completed within the isolated remote system (i.e., thecall is for a telephone also connected to the remote terminal or anothersubtended remote terminal), the controller of the switch proxy causesthe switching fabric to loop the call back to the remote terminal andthe causes the remote terminal to perform ringing and other suchfunctions as required to establish the call. The switch proxy continuesto monitor the transmission links towards the host switching system andwhen it ascertains that stable communications with that system have beenrestored, it initiates the process of dropping calls that it is carryingand reverts to monitoring, thus allowing the host switching system toresume providing service to the remote terminal. The switch proxy againtakes up the role of monitoring the trunk group between the hostswitching system and the remote terminal.

Importantly, the switch proxy's translation database is maintained by aswitch proxy management system, this translation database as a minimummaintains correspondence between a telephone subscriber's physicalappearance (port address) on the remote terminal and its telephonenumber. Advantageously, as subscribers are rearranged by the telephoneservice provider, change orders for several remote terminals may bereceived and processed by the same switch proxy management system. Theswitch proxy management system forwards relevant changes to each switchproxy's translation database. Further, maintenance and updates to theswitch proxy itself may be made in the same fashion. In this manner, alow-cost switch proxy may be used to maintain telephone service on aremote terminal when the remote terminal is disconnected from its hostswitching system.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of this invention may be obtained from aconsideration of this specification taken in conjunction with thedrawings, in which:

FIG. 1 is a block diagram of a wireline telephone system in which anexemplary embodiment of this invention is implemented;

FIG. 2 is a block diagram expanding on the details of FIG. 1;

FIG. 3 is a block diagram of an exemplary embodiment of the switch proxyof FIG. 1 and FIG. 2;

FIG. 4 is a state diagram illustrating the operational modes of a switchproxy;

FIG. 5 is a flow chart describing an exemplary embodiment of the controlfunctions of a switch proxy of FIG. 3;

FIG. 6 is a flow chart describing an exemplary embodiment of callprocessing functions of a switch proxy;

FIG. 7 is a block diagram illustrating the functional components of aswitch proxy management system; and

FIG. 8 is a flow chart illustrating the operation of the switch proxymanagement system of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a wireline local telephone network 100 inwhich an exemplary embodiment of this invention operates. In thewireline local telephone network 100 of FIG. 1, a local switching system102 (also referred to herein as local switch 102 or switching system102), typically residing in a central office 104 is connected throughtrunk group 106 to the public switched telephone network (PSTN) 108which provides for interconnectivity with subscribers worldwide. Thisconfiguration is used herein for convenience and clarity in describingthe invention; it is well known in the art that local switching system102 is part of PSTN 108. A plurality of telephone subscribers 110, 112may be connected directly to the local switching system throughsubscriber lines. Additionally, a plurality of subscribers 114, 116,118, and 120 may be supported from remote terminals 122 and 124 whichinterconnect to the local switch through trunk groups 126 and 128respectively. In the present context, a trunk group (also referred toherein as a trunk or trunks) consists of one or more physicaltransmission media (e.g., fiber optical cables or T1 lines) transportinga multiplicity of digital channels between network elements such as, butnot limited to, trunk group 126 between local switching system 102 andremote terminal 122. In general, remote terminals 122 and 124consolidate and concentrate signals to and from the customer telephones114, 116, 118, and 120 and connect these distant telephone subscribersto the local switch 102 over trunks 126 and 128 that have a capacity tosupport many voice and data channels over long distances. Such accesssystem remote terminals as 122 and 124 are also known in the art assubscriber loop carriers (“SLCs”) and digital loop carriers (“DLCs”) andare functionally referred to as remote terminals. In accordance withthis invention, a switch proxy 130 (illustrated herein in heavy blockline and described in more detail in conjunction with FIG. 3) residinglogically between the remote terminal 124 and the trunk 128 maintainstelephone services between subscribers 118 and 120 served by remoteterminal 124 when communications with local switch 102 is lost, forwhatever reason. In this manner, some basic services that formerly werenot provided when remote terminal 124 was isolated from local switchingsystem 102 are now available. For illustration purposes, assume thatremote terminal 124 provides service to a rural community many milesfrom local switching system 102. Further, assume that telephone 120 is atelephone at a local public safety provider, such as (but not limitedto) a local fire department or county sheriff's office. In the priorart, should communications with the local switch fail, a caller attelephone 118 could not contact telephone 120 in an emergency, eventhough both telephones are in the same community and the remote terminalis fully functional. In accordance with this invention, switch proxy 130takes over during an outage and provides at least limited local service.Thus, telephone 118 can be connected to telephone 120 in accordance withthis invention, even when local switching system 102 cannot provideservice.

FIG. 2 further illustrates some interface details of subscribers 110 and112 supported directly from switch 102, and subscribers 114, 116, 118and 120 deployed behind remote terminals 122 and 124 hosted by localswitch 102. Local switch 102 contains a switching fabric 202 thatinterconnects, on a channel-by-channel basis, a plurality of line units,herein represented by line units 204 and 206 and trunk units, hereinrepresented by trunk unit 208. These trunk and line unit subsystemsserve to adapt the circuits useful to the network, such as telephonelines, to a format that can be switched by switching fabric 202.Switching system 102, as is well known in the art, provides many otherfunctions such as billing and operator services, etc., which do notcontribute to the understanding of this invention and are thus notdescribed. Switching fabric 202, line units 204, 206 and trunk unit 208are all well known in the art, do not form part of the invention andthus are not further described.

A control unit 210 causes switching fabric 202 to connect a particularline (or member of a trunk group) to another based on informationcontained in translations database 212 which associates an internalphysical port address to a designation useful to the network, such as, atelephone number. When interfacing to access systems a special line unitcalled an integrated digital terminal (“IDT”) 214 can be used tointerface directly with digital trunks 126 to communicate with andcontrol remote terminal 122. An alternative approach is represented bythe use of a central office terminal 216 to convert a plurality ofsubscriber lines originating on line unit 206 into a multiplexed digitalsignal carried by digital trunk 128 that communicates to the remoteterminal 124. One skilled in the art will appreciate that the controlsignals embedded in trunks 126 and 128 must provide similar services andmay, in fact, be identical regardless of the methodology (e.g.,integrated digital terminal 214 or central office terminal 216) used tointerface to switch 102. These cases illustrate that the subscriberlines deployed using access systems do not differ significantly fromthose supported directly from switch line units in that they rely on thelocal switch for dialed digit collection, switching, translation, andother services.

As is standard in the art, control unit 210 of local switch 102 controlsall remote terminals (herein 122 and 124). Thus, when a telephone (suchas telephone 114) goes off-hook, remote terminal 122 detects theoff-hook condition and reports the off-hook condition to integrateddigital terminal 214. Integrated digital terminal 214 forwards theinformation to control unit 210. Control unit 210 causes switchingfabric 202 to provide dial tone through integrated digital terminal 214,digital trunk 126 and remote terminal 122 to telephone 114. Telephone114 then sends dual-tone, multifrequency signals (or dial pulses) backto control unit 210, which decodes the signals into dialed digits andperforms a look-up in translations database 212 to determine how tohandle the call. As is well known in the art, the local switch 102, bymeans of controller 210 controls the setup and tear down of all calls,whether originating or terminating on subtended remote terminals 122 and124. Signaling protocols are used between the access system remoteterminal and the central office components (e.g., remote terminal 122and integrated digital terminal 214, and remote terminal 124 and centraloffice terminal 216, respectively) to coordinate the connection andsignal the status of both ends. For example, GR-303 and GR-08, bothgeneric requirements (GR) published by Telcordia, Inc. and well known inthe art, are commonly used standards-based signaling protocols forproviding telephone service through remote terminals. While some remoteterminals (especially older remote terminals) use proprietary protocols,it is within the ability of one skilled in the art to build a switchproxy in accordance with whatever protocol may be used after studyingthis specification. The signaling uses bandwidth within the trunksinterconnecting the remote terminal and the host switch (e.g., trunk 126connecting host switch 102 and remote terminal 122) for messaging toconvey status and cause actions, these messaging channels are alsoreferred to as control signals.

FIG. 3 is a block diagram of switch proxy 130 illustrating certainexemplary aspects of this invention. In general, switch proxy 130comprises a trunk monitoring unit 314, a switching fabric 302interconnected with a trunk interface unit 304 by connections 305 andinterconnected with tones and receivers unit 318 by connections 316, abypass switch 312, and a controller 306 which coordinates the operationsof all of the subsystems. In this exemplary embodiment, switching fabric302 comprises a time slot interchange unit. One skilled in the art willappreciate that other types of switching fabrics (e.g., space divisionsolid state or metallic switches) may be employed to the same end.

In this exemplary embodiment, bypass circuit 310 is connected around theoperational units of switch proxy 130. Bypass circuit 310 includes anormally closed switch 312. That is, during normal operation of remoteterminal 124 under control of local switching system 102, bypass switch312 is closed and the switch proxy 130 is logically bypassed until suchtime as intervention is required. Thus, advantageously, failures withinthe switch proxy 130 are unlikely to affect normal operation of theremote terminal. A skilled practitioner of the art can suggest otherembodiments in which this bypass circuit is not required, such as, butnot limited to, passing the traffic actively from trunk 128 to trunk 132through switch proxy 130.

A trunk monitoring unit 314 is connected to trunk 128 in parallel withbypass circuit 310 on the central office terminal 216 side of switchproxy 130. Trunk monitoring unit 314 monitors trunk 128 for controlsignals from local switching system 102 and/or responses from remoteterminal 124 as well as alarm indications related to the serviceabilityof the trunk. When a service interruption is detected, trunk monitoringunit 314 notifies controller 306 while continuing to monitor trunk 128.Controller 306 causes switch 312 to open and begins to supervise trunk132 from remote terminal 124 by means of trunk interface unit 304.Controller 306 sends and receives control signals to/from telephonesconnected to remote terminal 124 by means of the control channelsembedded in trunks 132 in the same manner as local switch 102 doesduring normal operation. Based on information in these control signals,controller 306 causes switch fabric 302 to interconnect channelsassociated with subscribers in trunk 132 with the appropriate tones,dialed digit receivers and/or recorded announcements in tones andreceivers unit 318. After collection of the dialed information eitherthrough interpretation of rotary digits or from dual tonemulti-frequency digits received by the tones and receivers unit 318, thecontroller 306 consults the translation database 308 to determine if thecall can be completed within the subscriber base supported by remoteterminal 124 or another remote terminal (not shown) served by switchproxy 130. If the call can be completed, controller 306 causes switchingfabric 302 to connect one telephone to another. If it is not possible toroute the call (e.g., the subscriber is not served by a remote terminalsubtended to switch proxy 130) controller 306 causes switching fabric302 to connect the calling party to an appropriate tone or recordedannouncement supplied by tones and receivers unit 318.

Controller 306 uses data stored in translation database 308 to providesuch information as to determine what connections are possible as wellas to provide translations between physical port addresses and telephonenumbers. In addition, translation database 308 may contain informationthat would be useful to emergency responders such as, but not limitedto: subscriber name and address, GPS coordinates, and prioritizedemergency responders for each subscriber based on location. These data,or a subset thereof, in translation database 308 are synchronized totranslation database 212 in local switch 102 regarding telephonesconnected to remote terminal 124. Such synchronicity may be provided bya centralized switch proxy management system (which will be describedherein, below, in conjunction with FIG. 7) or manually through a localinterface to switch proxy 130. Two exemplary approaches to management ofthe switch proxy 130 are illustrated in FIG. 3: a centralized switchproxy management system 134 is interconnected to the remote switch proxy130 via communications means 136; alternatively, a local terminal 140(sometimes referred to in the art as a craft terminal) interconnectswith the switch proxy 130 through communications means 138.Communications means 136 and 138 can be, but are not limited to, dial-upmodem, Ethernet, or direct serial connection as is well known in theart.

An overview of the operational modes of switch proxy 130 are illustratedin FIG. 4 in conjunction with FIG. 3. As long as the remote terminal 124continues to communicate normally with the host switch as determined bytrunk monitoring unit 314, bypass switch 312 remains closed and thecontroller 306 operates in the bypass and monitoring mode 402 in FIG. 4.In this mode, the switch proxy 130 remains vigilant to the operationalstatus of the trunks as shown in decision loop 406 but does notintervene in the control of remote terminal 124. When trunk monitoringunit 314 concludes that the control signals between the host switch 102and remote terminal 124 have failed, controller 306 changes statethrough process 408 to the emergency stand alone mode 404 and takesaction to assume control of remote terminal 124. While the systemoperates in emergency stand alone mode 404, trunk monitoring unit 314continues to monitor the status of trunk group 128 and as indicated bydecision loop 412 will remain in emergency stand alone mode 404 as longas trunk group 128 cannot communicate with host switch 102. While inemergency stand alone mode 404, controller 306 causes bypass switch 312to open and asserts control of trunk 132 to remote terminal 124 by meansof trunk interface unit 304. When trunk monitoring unit 314 ascertainsthat trunk group 128 has returned to operational status, controller 306through process 410 restores the switch proxy 130 to bypass and monitormode 402. One skilled in the art will appreciate that momentary and/ortransient behaviors in trunk group 128 should not be cause for switchproxy 130 to transition between operational modes 402 and 404 or viceversa.

FIG. 5 expands on the details of FIG. 4 and provides an exemplaryembodiment of emergency stand alone operational mode 404. Processingbegins in bypass and monitoring mode 402. When trunks 128 between thehost switch 102 and the remote terminal 124 are no longer functional,decision block 406 passes processing to block 502 where bypass switch312 is opened and simultaneously in block 504 trunks 128 are conditionedinto an alarm state known in the art as “remote alarm indication” toassist in restoring service. In block 506 controller 306 by means oftrunk interface unit 304 asserts control of trunks 132 towards remoteterminal 124. In preparation for call processing and using theappropriate signaling protocol (e.g., GR-303) controller 306 in block508 establishes communications with remote terminal 124 and ascertainsand initializes the status (on-hook, off-hook, ringing, etc.) of thesubtended subscriber lines through an audit process. Continuing on toblock 510 switch proxy 130 now begins to process calls for remoteterminal 124 and remains in that mode until such time as service withthe host switch 102 has been restored. The status of these trunks isascertained by interrogating trunk monitoring unit 314 in decision block512. At such time as stable service in trunks 128 has been restored,processing transitions to block 514. In this exemplary embodiment inblock 514 the switch proxy does not terminate call processing servicesuntil such time as any ongoing 9-1-1 calls are completed, optionallythis block may be omitted. Processing in block 516 causes trunkinterface unit 304 to release trunk 132 (e.g., by entering into adisconnected or high impedance state) in preparation to restoringcontrol to the host switch 102 through trunk 128. Continuing with block518, bypass switch 312 is closed, restoring control of remote terminal124 to host switch 102 and subsequently switch proxy 130 returns tobypass and monitoring mode 402.

FIG. 6 expands upon the details of FIG. 5 and provides an exemplaryembodiment of the call processing block 510. For simplicity and as iscommon in the art, subscriber lines which originate a call are referredto as “calling” parties and those subscriber lines to which a call isplaced are referred to as “called” parties. As described in theforegoing discussion of FIG. 5, call processing block 510 is evokedafter establishment of the control of remote terminal 124 in theemergency stand alone mode 404. Beginning with block 602 wherein thecontroller 306 awaits a control message from remote terminal 124 throughtrunk interface unit 304 that a subscriber served by remote terminal 124has gone off-hook and therefore requires service. In the case of aconcentrating protocol (e.g., GR-303) switch proxy 130 then sends acontrol message to remote terminal 124 allocating a time slot on trunk132 for the calling (off-hook) subscriber to use. In block 604controller 306 connects the time slot allocated in the previous step totones and receivers unit 318 by means of switching fabric 302 wherebycalling party receives dial tone and has a digit receiver (both forrotary dialing and dual tone multi-frequency dialing, known in the artas an “originating register”) provided. After a proscribed number ofdialed digits have been collected, processing moves to block 606whereupon controller 306 interrogates translations database 308 as tothe status of the called party as represented by the dialed number. Forthe purposes of this discussion, decision block 608 interprets thestatus of called party in one of three ways, to whit: that called partyis on remote terminal 124 or other system (not shown) served by switchproxy 130, called party is not on a served system, or that called partyis 9-1-1. These three conditions require distinctive processing. Oneskilled in the art will understand that dial plans can be more complexthan in the aforementioned exemplary embodiment and can be accommodatedwithin the context of this invention.

Continuing on after decision block 608, should the called party not be asubscriber served by switch proxy 130 (i.e., “off system”) processingpasses to block 610 whereby controller 306 causes an appropriatecall-progress tone (e.g., “fast busy”) or recorded announcement fromtones and receiver unit 318 to be connected to the calling party throughswitching fabric 302. After the calling party returns to on-hook orafter a suitable time the call is cleared in block 612. If decisionblock 608 confirms that the called party is served by switch proxy 130(i.e., “on system”), processing is passed to block 614 whereupon thecall is classified as a “normal call” (i.e., not a 9-1-1 call) for theduration of the call.

Finally, if the result of decision block 608 is that the called party is9-1-1, processing is passed to block 616 whereupon the call isclassified as a 9-1-1 call and afforded special treatment for theduration of the call. Connection with the public safety answering point(“PSAP”), as would be the case when functional communications existsbetween remote terminal 124 and host switch 102, is not possible. Inaccordance with another aspect of this invention, translations database308 contains one or more 9-1-1 designates, such as a sheriff's office orfire department, which may be advantageously associated with a specificcalling party in order of preference. For example, the preferred 9-1-1designate for a given calling party may be the one that is nearest inproximity. Initially the preferential 9-1-1 designate for this callingparty is selected as the called party. If a 9-1-1 designate is busy on acall that is not a 9-1-1 call, the system will drop the existingnon-9-1-1 call and will quickly connect the incoming emergency call tothe 9-1-1 designate. Should processing return to block 616 as a resultof a failure to complete this call, successive 9-1-1 designates arechosen and the call attempt is repeated (i.e., a “hunt group”). Oneskilled in the art will appreciate that many alternatives to thisexemplary method of selecting alternative 9-1-1 designates to optimizethe response to the calling party are possible. For example, a pluralityof 9-1-1 designates could be simultaneously called and the first toanswer assigned the call. This simultaneous call approach is a favoredapproach because it potentially finds a 9-1-1 designate faster than thehunt group approach.

It should be noted that if a 9-1-1 designate had an answering machine,the switch proxy could deliver emergency calls to the 9-1-1 designate'sanswering machine with potentially disastrous results. Thus, 9-1-1designates should be instructed not to connect any answering machines to9-1-1 designate lines.

Whether a normal or 9-1-1 call, processing will transfer to block 618.Controller 306 communicates through trunk interface unit 304 to remoteterminal 124 the port address of the called party, obtained in blocks606 or 616 from translations database 308, and allocates a second timeslot on trunk 132 for the called party and communicates this with remoteterminal 124. Communications between controller 306 and remote terminal124 utilize control signals embedded in trunk 132 and the applicablesignaling protocol. Simultaneously remote terminal 124 is caused toinitiate ringing on the called party's line. Controller 306 causesswitching fabric 302 to connect the calling party time slot to an“audible ringing” tone via tones and receivers unit 318.

Also in accordance with another aspect of this invention, specialringing patterns and caller ID messages may be sent to the called partyin the event of a 9-1-1 call to advantageously alert the 9-1-1 designateas to the nature of the call. It is important that incoming emergencycalls be identified to the 9-1-1 designate so that they are managedcorrectly. For example, if an emergency call were to come in atsuppertime, and the 9-1-1 designate was unaware that the call was anemergency call, the designate may choose to ignore the call withpossible disastrous results. Therefore, the system provides incomingemergency calls with “distinctive ringing”, that is, a ringing signalwith an on/off pattern that is recognized as unique, so that the 9-1-1designate recognizes that the incoming call is an emergency call. Thisallows the 9-1-1 designate to give the call proper (urgent) answeringpriority and to answer the call with an appropriate greeting.

When an emergency arises and an emergency call is made over normallyoperational telephone company communication systems, the emergency callis delivered to a PSAP, as is discussed above. Along with the callitself, ANI and ALI information are also delivered to the PSAP emergencyoperator, so that the operator knows (as a minimum) the telephone numberand the address of the emergency caller and can dispatch emergencyresponders appropriately. This is important for a variety of reasons:because the caller may be hysterical, the caller may drop the telephone,the caller may become incapacitated, the call may be cut off, etc. Inthe switch proxy system described here, delivery of 9-1-1 callerinformation to a 9-1-1 designate is as important for the same reasonswhen in Emergency Stand Alone mode. In the present switch proxy system,the emergency caller's telephone number and name can be delivered usingconventional telephony caller identification (Caller ID) mechanisms. Inthis context, as is well known in the art, these means consist ofsending voiceband data signals containing the emergency caller'stelephone number and name in the transmission path from the switch proxyto the 9-1-1 designate during the silent interval between ringingbursts. The 9-1-1 designate needs to have a Caller ID display connectedto the 9-1-1 designated line to receive and display the callingtelephone number and name. In cases where the 9-1-1 designate needs onlyto be delivered the telephone number and name of emergency callers,conventional Caller ID equipment may be used.

In cases where it is desirable to deliver additional information, suchas but not limited to, the emergency caller's address, to the 9-1-1designate the designate line should have enhanced Caller ID equipmentwhich contains additional data receiving and displaying capabilities.Furthermore, the switch proxy should have the ability to identify,encode and send the additional information. The switch proxy databaseshould contain provisioning information indicating the capabilities ofindividual 9-1-1 designate's Caller ID equipment to optimize delivery ofemergency caller's supplemental information. By means of thisconventional and extended caller ID capability, the switch proxy in anadvantageous and novel manner provides essential information to the9-1-1 designate that hitherto would only have been available topersonnel at the PSAP.

In block 618, by means of an inquiry to database 308, the capabilitiesof 9-1-1 designates to receive information related to the calling partymay be ascertained and appropriate data signals sent as part of the“alerting” process towards the called party or parties. In the exemplaryembodiment of FIG. 3, when operating in ESA mode and a time slot hasbeen established between the 9-1-1 designate and the trunk interfaceunit 304, controller 306 may cause these data signals to be sent fromtones and receivers unit 318 by means of switching fabric 302.

The clearing of a stable call, represented by block 622, is addressed inblock 628 and requires particular attention in this exemplary embodimentin that it is advantageous to treat disconnection of normal calls and9-1-1 calls differently. Whereas it is acceptable to clear stable callsof the “normal” type whenever either party returns to an on-hook state;control of the disconnection of a 9-1-1 call should, at leastoptionally, be the sole prerogative of the called party (i.e., the 9-1-1designate). That is, should the calling party in a 9-1-1 callprematurely go on-hook it is desirable that the calling party be able toreturn to off-hook and continue the conversation with the 9-1-1designate until such time as the called party goes to an on-hook state.This is known in the art as “called party control”.

Under this “called party control,” the connection between the emergencycaller and the 9-1-1 designate does not get torn down when the emergencycaller hangs up. It requires the 9-1-1 designate to hang up before thecall is torn down. Thus, for example, if the emergency caller hangs upand tries to make another call while the 9-1-1 designate stays on thefirst call, the emergency caller is reconnected to the 9-1-1 designateas soon as the emergency caller goes off hook.

One last functional block in FIG. 6 needs to be addressed. All callscleared from the system during ESA operation, regardless of cause, passfrom block 612 onto block 630 which generates a record of the call foraudit purposes. These records, known in the art as Call Detail Records(CDRs), contain information related to each call attempt which mayinclude but is not limited to: calling and called party numbers, outcomeof the call attempt, time and duration of the call, etc. These CDRsdocument the system operation while disconnected from the host switchingsystem and afford some liability protection. The CDRs may be optionallyretrieved from the switch proxy locally or archived throughcommunications with the switch proxy management system.

In each of these cases it is necessary for the switch proxy to haveaccess to a database containing port identifiers, names, telephonenumbers, and optionally, supplemental information to support thesefeatures. The information in this database may be collected in severalways. Since the information needed is available in existing telephonecompany and public safety databases, it may be collected by searchingfor and retrieving the needed information in those databases. A similarmanual mechanism can be used if the information needed is available inprinted or on-line reports. In this case, a clerk periodically updatesthe database in the switch proxy management system (described herein,below, in conjunction with FIG. 7 and FIG. 8), based upon these reports.Once compiled, the information may periodically be downloaded to theswitch proxy for use during Emergency Stand Alone mode. A mechanism forlearning the telephone number of each port identifier in a DLC systemusing test calls has been described elsewhere. However, any name andaddress information will need to be collected from external databasesand provided to the switch proxy either manually or automatically via amechanized data delivery system. Because telephone systems areconstantly changing as a result of responding to service orders, it isnecessary to update these data in a timely way to insure that they arecorrect. Failure to update the switch proxy database in a timely waycould result in sending emergency responders to incorrect locations withpotentially disastrous results.

FIG. 7 is a block diagram of an exemplary embodiment of a switch proxymanagement system 134 in accordance with another aspect of thisinvention. This switch proxy management system 134 generally comprises adatabase 704 and a communications unit (or units) 706, all responsive toprocessor 702. At least one file is kept for each switch proxy indatabase 704, wherein translations records for each line (such as lines118 and 120) served by a switch proxy 130 are maintained. At a minimum,these records correlate the physical port address of the subscriberlines on the remote terminal with the telephone number. Additionalinformation which may be associated with the subscriber line include,but are not limited to: name and address of the subscriber, emergencyresponders contact telephone numbers, and related information that wouldbe useful during an emergency. This database may also be used tomaintain operational information related to each switch proxy such as,but not limited to: configuration data, current software loads,aforementioned Call Detail Records, and time zone. Database 704 must beinitially populated correctly and then maintained current, mostimportantly with respect to subscriber changes. This may be donemanually (through e.g., management console 708) or in an automatedfashion by reference to other databases that are maintained for otherpurposes such as, but not limited to, the service provider's operationalsupport system or billing system through interface 710, or third-partydatabases such as those maintained by 9-1-1 database providers throughinterface 712. Said service provider's operational support system may bethe same system that keeps translation database 212 of local switch 102current.

The operation of switch proxy management system 134 will now bedescribed in the context of the flow chart of FIG. 8 taken inconjunction with the block diagram of FIG. 7. Processing starts incircle 800. In block 802, controller 702 causes communications unit 706to interrogate external databases through interfaces 710 and 712 andmanagement console 708 for changes. Processor 702 determines whether thedata affects any line served by a switch proxy by comparing the datareceived to data in database 704 in decision block 804. If no changeaffecting any switch proxy is detected, then processing loops back toblock 802 and the change is ignored.

If, in decision block 804, a change affecting one or more lines servedby a switch proxy is detected, then a database lookup is performed onthe affected line or lines in block 806. Changes are recorded indatabase 704 in block 808. Finally, all changes are transmitted to theaffected switch proxy via communications unit 706. The changes may betransmitted when discovered or may be transmitted as a batch job duringnon-peak times.

While this exemplary embodiment is described in terms of a directconnection between switch proxy management system 134 and one or moreswitch proxies and external databases through interfaces 710 and 712,one skilled in the art will appreciate that there are many ways toprovide this interconnection. For example, these connections may be overdial-up modems, Ethernet, or proprietary telemetry networks.

It is to be understood that the above-described embodiments of thisinvention are merely illustrative of the present invention and that manyvariations of the above-described embodiments can be devised by oneskilled in the art without departing from the scope of the invention. Itis therefore intended that such variations be included within the scopeof the following claims and their equivalents.

1. A switch proxy for controlling a remote terminal when said remote terminal is isolated from its controlling local switching system, wherein the remote terminal is connected to the controlling local switching system by a trunk and supports a plurality of subscriber telephone lines, said switch proxy comprising: a controller; a translations database maintaining translations for switching calls among the subscriber telephone lines supported by the remote terminal, said translation database further maintaining translations for switching 9-1-1 calls from subscriber telephone lines to 9-1-1 designates supported by the remote terminal; and a switching fabric controlled by the controller and said translations database to switch calls among the subscriber telephone lines supported by the remote terminal when connection between the remote terminal and the local switching system is lost.
 2. The switch proxy of claim 1 further comprising a trunk monitoring unit monitoring control signals between the local switching system and the remote terminal on said trunk and notifying the controller whenever connection between the remote terminal and local switching system has been lost.
 3. The switch proxy of claim 1 further comprising a trunk monitoring unit monitoring alarm signals on said trunk between the local switching system and the remote terminal and notifying the controller whether connection between the remote terminal and local switching system has been lost.
 4. The switch proxy of claim 1 further comprising a bypass switch responsive to the controller on said trunk between the local switching system and the remote terminal that removes the switch proxy from active participation in the transmission path until required.
 5. The switch proxy of claim 1 further comprising a tones and receivers unit responsive to the controller that receives dual tone multi-frequency dialing and provides call progress tones, recorded announcements, and caller ID data signals for subscriber telephone lines supported by the remote terminal(s).
 6. The switch proxy of claim 1 wherein 9-1-1 calls are routed to a hunt group containing a plurality of 9-1-1 designates.
 7. The switch proxy of claim 1 wherein 9-1-1 calls are simultaneously routed to a plurality of 9-1-1 designates and the first 9-1-1 designate to answer is assigned the call.
 8. The switch proxy of claim 1 wherein distinctive ringing is used for a 9-1-1 call routed to a 9-1-1 designate.
 9. The switch proxy of claim 1 wherein traditional caller ID information (calling number and name) for the 9-1-1 call is provided to the 9-1-1 designate.
 10. The switch proxy of claim 1 wherein supplemental information for the 9-1-1 call is encoded within the caller ID format and received by the 9-1-1 designate using special receiving apparatus.
 11. The switch proxy of claim 1 wherein the 9-1-1 designate is provided with called party control of the 9-1-1 call.
 12. The switch proxy of claim 1 wherein the switch proxy interrupts an existing normal (not a 9-1-1) telephone call to the 9-1-1 designate prior to connecting the 9-1-1 call.
 13. The switch proxy of claim 1 wherein a record relating to the details each call originated during ESA mode is created and archived for later retrieval.
 14. A method for controlling a remote terminal when said remote terminal is isolated from its controlling local switching system, wherein the remote terminal is connected to the local switching system by a trunk and supports a plurality of subscriber telephone lines, said method comprising: monitoring the trunk for alarms and/or local switching system/remote terminal control signal dialogue to determine whether the remote terminal is isolated from the local switching system; maintaining a translations database containing information for switching calls among the subscriber telephone lines supported by the remote terminal, said translations database also including translations for switching 9-1-1 calls from subscriber telephone lines to 9-1-1 designates supported by the remote terminal; and switching calls among the subscriber telephone lines supported by the remote terminal when the remote terminal is isolated from the local switching system.
 15. The method of claim 14 further comprising operating a bypass switch on said trunk between the local switching system and the remote terminal that removes the emergency stand alone apparatus from active participation in the transmission path until required.
 16. The method of claim 14 wherein 9-1-1 calls are routed to a hunt group containing a plurality of 9-1-1 designates.
 17. The method of claim 14 wherein 9-1-1 calls are simultaneously routed to a plurality of 9-1-1 designates and the first 9-1-1 designate to answer is assigned the call.
 18. The method of claim 14 wherein distinctive ringing is used for a 9-1-1 call routed to a 9-1-1 designate.
 19. The method of claim 14 wherein caller traditional ID information (calling number and name) for the 9-1-1 call is provided to the 9-1-1 designate.
 20. The method of claim 14 wherein the 9-1-1 designate is provided with called party control of the 9-1-1 call.
 21. The method of claim 14 wherein the switch proxy interrupts an existing normal (not a 9-1-1) telephone call to the 9-1-1 designate prior to connecting the 9-1-1 call.
 22. The method of claim 14 wherein supplemental information for the 9-1-1 call is encoded within the caller ID format and received by the 9-1-1 designate using special receiving apparatus.
 23. The method of claim 14 wherein a record relating to the details of each call originated during ESA mode is created and archived for later retrieval.
 24. A method for controlling a remote terminal when said remote terminal is isolated from its controlling local switching system and a subscriber originating a 9-1-1 call has been detected on said remote terminal, said method comprising: determining the line identification of the subscriber from which the digit signals 9-1-1 were received; selecting at least one 9-1-1 designate to which to connect the 9-1-1 call based on the determined line identification using a translations database; and connecting the 9-1-1 call to the selected 9-1-1 designate.
 25. The method of claim 24 further comprising selecting a 9-1-1 designate to connect by traversing a hunt group consisting of a plurality of 9-1-1 designates to ensure that the 9-1-1 call is completed.
 26. The method of claim 24 further comprising providing the 9-1-1 designate with called party control over the 9-1-1 call. 